Create a "global" value for multiple settings
Well, you need to know about Drivers.

Drivers are scripts which main purpose is to control properties with other properties. In example the rotation of one object is controlled with the location of another object.

Drivers can use properties, numbers, transformations, and scripts, to control the values of properties.

Using a F-Curve, the driver reads the value of the Driver Value and sets the value of the selected property it was added to.
So for example, if the Driver Value is 2.0 the property can be 0.5.

https://docs.blender.org/manual/ru/dev/animation/drivers/introduction.html